1. Field of the Invention
The present invention relates to a video signal recording and reproducing apparatus for recording a video signal after adding thereto a specific signal necessary for recording the video signal on a recording medium.
2. Description of the Prior Art
In a video tape recorder or the like for recording and reproducing video signals, in order to alleviate the so-called triangular noise characteristic of FM transmission line noise in a frequency modulation and demodulation system, the signal level is raised in the medium and high frequency regions in the recording system by an emphasis processing, and lowered in the medium and high frequency regions in the reproducing system by de-emphasis processing.
Recently, moreover, in order to record a wideband video signal, a time axis compression multiplexing and multi-channel recording of the luminance signal and chrominance signal is employed. In this recording, generally, only an effective period containing a luminance signal (Y) and a chrominance signal (C) of an input video signal is taken out, and added to a specific signal which is necessary for recording the video signal, such as a synchronous signal and a Y/C guard signal.
FIG. 5 shows a conventional processing circuit. FIG. 6 is a waveform diagram showing signals at some portions in FIG. 5. In this example, the emphasis is a phase linear emphasis, but it may be a phase nonlinear emphasis.
In FIG. 5, element 1 is a luminance signal input terminal element 2 is a chrominance signal input terminal element 3 is a time-division multiplex (TDM) encoding circuit for time-compressing and multiplexing the luminance signal and chrominance signal to obtain a TDM signal; element 21 is an emphasis circuit; element 6 is a signal addition circuit for adding a specific signal necessary for recording; element 7 is a recording processing circuit for converting the TDM signal into a recordable signal suited to recording; element 8a is a recording head, for recording the recordable signal on a magnetic tape 9; element 8b is a reproducing head for reproducing the recorded signal from the magnetic tape 9; element 10 is a reproduction processing circuit for processing a reproduced signal from the head 8b to obtain the TDM signal; element 22 is a de-emphasis circuit; element 13 is a TDM decoding circuit for separating the TDM signal from the de-emphasis circuit 22 into the luminance signal and chrominance signal; element 14 is a synchronous signal addition circuit for adding a synchronous signal to the reproduced video signal (each of the luminance and chrominance signal); element 15 is a luminance signal output terminal, and; element 16 is a chrominance signal output terminal.
When recording, luminance and chrominance signals of a colorless and black level video signal, for example, as shown in waveform diagrams a and b in FIG. 6 are fed to the luminance signal input terminal 1 and chrominance signal input terminal 2, respectively. Here, t4 is the effective period of the luminance signal, and t2 is the effective period of the chrominance signal. The luminance signal and chrominance signal are compressed and multiplexed on the time axis in the TDM encoding circuit 3 to become a TDM signal as shown in c in FIG. 6. Here t1 is the synchronous signal period, t2 is the effective period of the chrominance signal, t3 is the Y/C guard period, and t4 is the effective period of the luminance signal. Usually black level signals are inserted in t1 and t3. The TDM signal becomes a waveform increased in the medium and high frequency regions as shown in d in FIG. 6 after passing through the emphasis circuit 21. In the recording signal addition circuit 6, the TDM signal is added to a synchronous signal in t1 and a Y/C guard signal in t3 to be the waveform as shown in e in FIG. 6. This signal is converted into a recordable signal suited to recording in the recording processing circuit 7, and then recorded on the magnetic tape 9 by the recording head 8a.
When reproducing, the signal reproduced by the reproducing head 8b is converted into the TDM signal by the reproduction processing circuit 10. The reproduced TDM signal is entered in the de-emphasis circuit 22, and decreased in level in the medium and high frequency regions decreased as shown in waveform f in FIG. 6. In the TDM decoding circuit 13, from the TDM signal f in FIG. 6, the signals in the effective period t4 of the luminance signal and the effective period t2 of the chrominance signal are separated, and expanded on the time axis. Then after adding a synchronous signal to each of the reparated luminance and chrominance signals in the synchronous signal addition circuit 14, the luminance signal g shown in FIG. 6 is ourputted from the luminance signal output terminal 15, and the chrominance signal h shown in FIG. 6 is outputted from the chrominance signal output terminal 16.
During recording, the specific signals necessary for recording, i.e., the synchronous signal and Y/C guard signal, are added to the signals in the periods t1 and t3 in FIG. 6d which contain the impulse responses due to emphasis processing of the chrominance signal and luminance signal in the effective periods t2 and 4t. When reproducing, the de-emphasis processing is done while the synchronous signal and Y/C guard signal are being added. Accordingly, there is a problem in that the waveform as in FIG. 6h has a deteriorated end portion of the effective period t2 of the chrominance signal. It may be considered advisable to insert a colorless signal level into the synchronous signal period t1 and Y/C guard signal period t3 of the signal in FIG. 6c before the emphasis processing in during recording, but in such a case the waveform deteriorates in the end portion of the effective period t4 of the luminance signal.